Methane gas hydrates have stimulated substantial international interest due to their potential as a future energy resource, but furthermore as a geotechnical hazard for offshore operations related to hydrocarbon recovery. In this context, the ability to quantify and detect the presence and concentration of hydrate in marine sediments and understand the effects it has on these host sediments has become increasingly important. The detection and quantification of gas hydrates and their effect on hydrate-bearing sediments has been inferred via exploratory seismic methods, which measure indirectly the bulk dynamic properties of sizeable volumes of in situ sediment. Traditionally, effective medium models are used to interpret the seismic data by employing theoretical assumptions that relate gas hydrate content within the sediment to wave velocities. Therefore, wave velocity can be used to deduce hydrate concentration levels. The modelling of methane gas hydrate-bearing sediments is relatively new and at present has been based on theories of rock physics and effective medium modelling. A variety of such models exists in the literature. Many effective medium models are not readily transferable to other settings, as they have been calibrated on and tested on specific sites. In addition, many models do not take into account the existence of heterogeneities of the host sediment, or the inhomogeneous distribution or formations of hydrate within the sediment. This paper presents a general review of the existing effective medium models, identifying typical areas for improvement. A new numerical modelling method is presented that can specifically take into account different hydrate morphologies within the host sediment thereby enhancing the existing effective medium models. Preliminary results from the numerical model are presented, portraying the impact of hydrate on the mass seismic properties of the host sediment.